1. Field of the Invention
The subject invention relates to printing equipment and, more specifically, to wrap-on printing plates and to methods and apparatus for producing same.
2. Disclosure Statement
The following disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior art, inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness, and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material though not necessarily being of itself pertinent. Also, the following comments contain conclusions and observations which have only been drawn or become apparent after conception of the subject invention or which contrast the subject invention or its merits against the background of developments which may be subsequent in time or priority.
Rotogravure printing is becoming increasingly preferred over offset printing where fine printing quality is important, especially for long printing runs. Rotogravure printing also turns out to be more economical than offset printing, when high quality is to be maintained throughout extremely long runs.
However, unlike offset printing, rotogravure printing has lacked flexibility. In this respect, recent years have seen an increasing demand for items of regional interest and for local advertisements in national newspapers and periodicals. This demand has been paralleled by an increasing need for effective language or text changes, or listings of such items as prices and firm names, in larger, otherwise unaltered catalogs or other texts. These and other changes in copy, page insertions and regional advertisements are costly to the gravure printer in production time and expense.
A solution to this problem has been seen in providing a rotogravure system with exchangeable printing plates which may be wrapped onto the printing cylinder so as to permit localized changes to be effected thereon without replacement of an entire printing cylinder. The term "wrap-on" is employed herein generically, to extend at least to wrap-around plate systems and to systems in which the plate is only wrapped on part of the circumference of the cylinder.
In this respect, wrap-on blankets have been known for a long time in offset printing. However, such blankets, as well as similar approaches, were not suitable since they inherently left large gaps where the blanket or similar structure was attached to the printing cylinder, as may, for instance, be seen from U.S. Pat. Nos. 1,074,775, by G. R. Cornwall, issued Oct. 7, 1913, for an offset blanket, 1,275,877, by C. E. Drange, issued Aug. 13, 1918, for a plate printing machine, 1,565,216, by C. N. Smith, issued Dec. 8, 1925, for an electroplated stero-type plate, 1,750,562, by P. Allman, issued Mar. 11, 1930, for a printing surface, 2,108,822, by W. L. Lippincott, issued Feb. 22, 1938, for a printing plate and formation thereof, 2,305,852, by H. N. Durham, issued Dec. 22, 1942 for a stereo-type printing plate, 2,953,091, by H. J. Luehrs, issued Sept. 20, 1960, for plate clamping means for wraparound printing plates, 3,230,883, by M. Achinger et al, issued Jan. 25, 1966, for a printing press plate clamping mechanism, 4,178,402, by F. Klapproth, issued Dec. 11, 1979, for a cylinder blanket for offset printing presses, and 4,227,459, by W. Jeschke, issued Oct. 14, 1980, for a transfer drum for rotary printing presses, and French Pat. Nos. 553.002, by Societe Anonyme des Anciens Etablissements Marinoni et Voirin Reunis, issued Feb. 1, 1923, for devices for installing plates on rotary printing cylinders and 1.044.012, by Marinoni S. A., issued June 17, 1953, for rotary printing plate tensioning mechanisms.
There also is a line of proposals which uses part of the printing plate itself for tensioning purposes as may, for instance, be seen from U.S. Pat. Nos. 2,131,891, by W. F. Huck, issued Oct. 4, 1938, for a printing plate having spaced apertures or recesses for engagement by locking fingers 2,630,756, by J. O. Crabtree et al, issued Mar. 10, 1953, for printing plates having projections and recesses for engagement by retention devices, 3,029,730, by J. R. Parrish et al, issued Apr. 17, 1962, for a method of forming laminated printing plates with plastic cores having grooves for cooperation with securing clamps, 3,490,369, by W. F. Huck, issued Jan. 20, 1970, for a printing cylinder and plate securing interlocking system, and 3,976,005, by H. Kaufmann, issued Aug. 24, 1976, for a printing plate having indentations for plate securing purposes, and German Published Patent Application Auslegeschrift No. 1 092 035, by L. Horn, published Nov. 3, 1960, and disclosing a tensioning mechanism for stereo-type plates in which locking fingers engage corresponding recesses in the printing plates. By way of general comment, proposals of the type shown in these references would be restricted to plates of considerable thickness.
Similar considerations apply to proposals in which a bent portion of the printing plate itself is grabbed for tensioning and retention thereof on a printing cylinder, as may, for instance, be seen from U.S. Pat. Nos. 2,775,198, by T. H. Johnson et al, issued Dec. 25, 1956, for a plate clamp, and 4,214,530, by J. A. Signorelli et al, issued July 29, 1980, for a metal printing plate, French Pat. No. 1.115.946, by A. Cuny, issued Jan. 23, 1956, for printing plates tensioning devices, and German Pat. No. 617 936, by Schnellpressenfabrik Koenig & Bauer A. G., issued Feb. 6, 1934, for a mechanism for tensioning flexible printing plates on a form cylinder.
A series of proposals for attaching a wrap-around printing plate to a printing cylinder with the aid of folded over margins of the printing plate is apparent from U.S. Pat. No. 1,049,195, by W. H. Banzett, issued Dec. 31, 1912. The very complex clamping apparatus for tensioning locked printing plates disclosed in U.S. Pat. No. 2,474,127, by P. L. Tollison et al, issued June 21, 1949, appears to fall into the same category.
Bending off the ends of a printing plate sharply and pulling them inwardly into the printing cylinder in practice leaves gaps which have to be filled in some manner in order to avoid strong visible gap marks on the printed work. Reference may in this respect be had to U.S. Pat. No. 1,795,700, by G. T. Baldwin, issued Mar. 10, 1931, for a mechanism for securing flexible plates to printing cylinders, to its corresponding Italian Pat. No. 296 395, issued Mar. 16, 1932, to U.S. Pat. No. 1,996,348, by L. T. A. Robinson, issued Apr. 2, 1935, for a complex multi-segment print cylinder arrangement with wrap-on printing plate, to its corresponding German Pat. No. 567 546, issued Feb. 21, 1931, to British Patent Specification No. 840,586, by F. H. Levey Company, Inc., published July 6, 1960, and disclosing clamping devices for printing presses employing sharply downturned printing plate margins, and Swiss Pat. No. 146 573, by Vogtlandische Maschinen-Fabrik A. G., issued Apr. 30, 1931, for a form cylinder for rubber printing machines in which the margins of the printing plate are also turned inwardly at an acute angle and a bar has to be employed in an attempt to close the gap between the outward printing plate end portions. These and other proposed methods for closing printing plate gaps are, however, either practically ineffective or cumbersome and time consuming, just like the casting of the plate butt, shown in German Patent Publication Offenlegungsschrift No. 24 09 456, by H. Kurtz, published Aug. 28, 1975, for rotary printing cylinders, and the abstract of German Utility Model Registration No. 75 25 069.
German Pat. No. 541 478, by Mashinenfabrik Johannisberg G.m.b.H., issued Dec. 30, 1930, shows a device for clamping flexible printing plates on the form cylinder of intaglio printing presses where the bent-off ends of the printing plates are held in clamping strips and stressed by means of a wedge both in radial and in tangential directions. This device is only suitable for form cylinders which have the width of the printing plates, and it has a disadvantage that the form cylinder must be removed from the machine to change the printing plates, since the clamping strips and the wedge can only be introduced into the dove-tailed grooves at the front end.
A proposal which is even more impractical for present purposes is apparent from U.S. Pat. No. 1,807,637, by E. Sachs, issued June 2, 1931, and proposing the provision of a helical dove-tailed groove over the circumferential surface of a printing cylinder of aluminum or another light metal. A strap, ribbon or wire of copper or other well-conducting metal, is forced into that groove to become wedged therein and to extend therealong also in a helical fashion. A metal layer serving as the etching ground is then placed upon the surface of the light metal cylinder. Such metal layer, which may, for instance, be a copper coating, thereby is supposed to be firmly connected with the helical metal strap, ribbon or wire. Of course, if such a procedure were followed for present purposes, the metal layer or printing plate could not be removed from the light metal printing cylinder, but would be permanently affixed thereto, which would defeat the object of interchangeability of printing plates relative to a printing cylinder. In that respect, the latter Sachs proposal follows in effect the teaching of U.S. Pat. No. 789,342, by F. A. Voelke, issued May 9, 1905, for a process of construction seamless, hollow articles in which a seamless spherical or hollow-cylindrical shell is permanently and irremovably plated on internal bracing plates.
In this respect, reference may also be had to U.S. Pat. No. 3,359,898, by F. L. Baier et al, issued Dec. 26, 1967, for process of preparing electro-type printing plates, U.S. Pat. No. 3,676,040 by P. W. McKinney, issued July 11, 1972, for apparatus for producing trimmed printing face plates, U.S. Published patent application No. B 462,424, by L. C. McCandless, published Feb. 24, 1976 and disclosing a method of making reinforced composite structures employing electroforming technology, British Patent Specification No. 694,141, by O. Evans, published July 15, 1953, and disclosing an electrotyper's case for the electrodeposition of curved shells, and British Patent Specification No. 1 537 243, by A. O. Jakubovich et al, published Dec. 29, 1978, and disclosing the production of iron foil by electrodeposition.
Against this background, it is well to recall the basic requirements that have to be met for a satisfaction of the above mentioned needs and demands.
Briefly, care must be taken that the flexible printing plates are clamped tightly and uniformly on the cylinder body, and that the butt joint is closed completely so that no ink can be deposited therein and so that the wiper or doctor blade can slide smoothly over it, whereby no objectionable trace of the plate edges appear on the printed copy. In other words, the printing plates have to abutt each other in a gapless fashion, be individually replaceable or exchangeable, be positioned firmly on the form cylinder so as to avoid a lifting thereof during the printing process, and be maintained in their position on the form cylinder with high precision.
Against this background, I invented the form cylinder and flexible printing plate disclosed, for instance, in my U.S. Pat. No. 4,157,067 issued June 5, 1979 and incorporated herewith by reference herein.
My invention according to that patent employed clamping bar mechanisms for attaching wrap-on printing plates to form cylinders, and proposed several techniques for joining the printing plate body to the clamping bars, and for minimizing any gap between adjacent printing bars or between any printing bar and an adjacent printing cylinder surface.
While these proposals and their practical implementation represented a substantial advance in the art, there was still room for improvement in terms of attainable printing quality. Moreover, the manner of attachment of the clamping bar on the printing plate as disclosed in my prior patent is by its nature time-consuming and in need for frequent reworking and finishing.